The purpose of the presented study was the experimental measurement of lumbar spine stiffness and its range of motion. The dependence of torsion moment of lumbar spine segment on deflection of flexion, extension and torsion was observed during experiments. Stiffness of spine segment was determined from measured data. Human lumbar spine was used for verification of the experimental technique. The sample consisted of one lumbar vertebrae composed by five vertebral bodies and four intervertebral discs. All muscles were removed, however all ligaments were preserved. Experiments were ca rried out on the test system MTS 858.2 MiniBionix, where loading by axial force and torsion moment is possible at the same time. Special Modular Bionix Spine Test Fixator, attached to the test system was used for the measurements. Loading was controlled kinematically (gradual turning) by keeping the axial force equal zero. Measurement was timedependent. The results of these experiments are going to be used as input data for creating a model of artificial lumbar spine and new type of artificial disc replacement

Horák, Z.

Jirková, L.

Michalec, J.

Sedláek, R.

Stoffel, M.

Tichý, P.

Weichert, D.

University of Queensland eSpace

5th Australasian Congress on Applied Mechanics, ACAM 2007  
10-12 December 2007, Brisbane, Australia 
Preliminary measurements of lumbar spine kinematics and stiffness  
 
L. Jirková1, Z. Horák1, R. Sedláek1, P. Tichý1, J. Michalec1, D. Weichert2, M. Stoffel2 
 
1Czech Technical University in Prague, Faculty of Mechanical Engineering, Department of Mechanics, 
Biomechanics and Mechatronics; Prague, Czech Republic  
2RWTH Aachen University, Faculty of Mechanical Engineering, Department of General Mechanics; 
Aachen, Germany  
Abstract: The purpose of the presented study was the experimental measurement of lumbar spine 
stiffness and its range of motion. The dependence of torsion moment of lumbar spine segment on 
deflection of flexion, extension and torsion was observed during experiments. Stiffness of spine 
segment was determined from measured data. Human lumbar spine was used for verification of the 
experimental technique. The sample consisted of one lumbar vertebrae composed by five vertebral 
bodies and four intervertebral discs. All muscles were removed, however all ligaments were 
preserved. Experiments were ca rried out on the test system MTS 858.2 MiniBionix, where loading by 
axial force and torsion moment is possible at the same time. Special Modular Bionix Spine Test 
Fixator, attached to the test system was used for the measurements. Loading was controlled 
kinematically (gradual turning) by keeping the axial force equal zero. Measurement was time-
dependent. The results of these experiments are going to be used as input data for creating a model 
of artificial lumbar spine and new type of artificial disc replacement.  
Keywords: spine, lumbar, artificial, kinematics, stiffness 
1 Introduction 
The lumbar instability is a common disease in clinical practice. Degenerative changes in the discs are 
always accompanied by osteophyte formation on the margins of the vertebral bodies and remodelling 
changes in the apophyseal joints. There is a direct relationship between the degree of disc 
degeneration, marginal osteophyte formation on vertebral bodies and apophyseal joint changes, what 
means that disc degeneration is the primary event leading to the clinical condition degenerative 
spondylosis. There are two surgical methods in treating the disc degeneration (when replacing 
intervertebral disc): spinal fusion and artificial discs. Disadvantage of fusion is the decrease of mobility 
in dependence on increase of adjacent vertebrae stability and disc load. None of the currently 
available artificial intervertebral discs respects all properties of natural disc (no shock absorption, no 
bending and torsion stiffness). Therefore surgeons demand development of a new artificial disc, which 
will respects all physiological properties of intervertebral disc. The aim of this project is experimental 
measurement of lumbar spine kinematics and stiffness. The main problem of this experimental study 
is the availability of cadaveric human spine specimens concerning ethics, legislation and other 
problems. Therefore it is a necessary to develop an artificial model which respects all physiological 
properties of the human lumbar spine, which will be tested instead of real human spine. Therefore, 
both of these measurements must be in progress simultaneously to determine appropriate function of 
artificial model. These experimental results will be used as input data for c reating a new type of 
artificial disc replacement which is going to be developed. 
2 Testing Procedure 
2.1 Principle of measurement 
Experiments were carried out on a special spine fixator with six degrees of freedom attached to the 
test system MTS 858.2 MiniBionix (fig. 1). Loading by axial force and moment was possible at the 
same time. Modular Bionix Spine Test Fixture allows performing a wide variety of spinal column 
kinematics studies. Bending moment, axial loads, or a combination of torsion or flexural motions can 
be measured. The fixture includes multi-channel and axial/torsion systems for analyzing both skeletal 
and soft tissues during surgical treatment. Servohydraulic Bionix Spine Test Fixture operates with low 
friction and high stiffness, resulting in high-response and high-performance tests that closely simulate 
  
the human spine behaviour. Kinematics measurements such as extension/flexion, medial/lateral and 
internal/external rotation can be carried out by the Spine Simulator. 
The motion segment was loaded by pure bending moment in flexion and in extension and by a 
moment about the z-axis (in torsion). Loading was controlled kinematically (gradual turning) by 
keeping the axial force equal zero. Range of motion was controlled by the spine fixator in interval (+ 
5.3 :  -6.3 deg) by flexion/extension. Specimen was loaded just in one direction up to the maximal 
angle of +1.3 deg in torsion [9]. The response of the specimen [Nm] was measured and stiffness was 
determined. 
 
Figure 1 - MTS-Spine fixator. 
Application of load was static without inertial forces. In this case just one unembalmed human 
cadaveric lumbar spine (five vertebral bodies L1-L5) was used. The specimen remained frozen to -
20°C until was measured. Tensile forces from muscles were simulated by applying a bending moment 
[11]. Mobility and stiffness were measured in dependence on time.  
Resulting stiffness k was determined by (1), where Mc is a general moment and j is the rotation angle. 
1N.m.degc
M
k
j
-é ù= ë û  (1) 
2.2 Development of new type of artificial disc replacement and model of artificial 
lumbar spine 
Development of new type artificial disc replacement depends on an input data which havent been 
measured completely yet. The artificial model of the lumbar spine has to be assembled according to 
real physiological properties of the human lumbar spine. This model has to be in accordance with 
geometry, mechanical properties of bones, ligaments and intervertebral discs. Materials of constituent 
elements were chosen independently on its biocompatibility. Mechanical properties of bone are 
discussed in [1]. There is a considerable difference of values of biomechanical parameters and 
material properties of lumbar spine ligaments depending on source [2  8]. Geometry of bone parts 
was generated directly from CT data and on its basis the model was made. Figure 2 shows the 
construction of a various types of the lumbar spine ligaments. 
  
 
Figure 2 - Anatomy of the lumbar spine [12]. 
Advantage of this model is the independence of experimental measurements on the human spine 
specimen source. Combination of a various materials with same mechanical properties of a human 
spine and taking into account the comparison of surgical techniques influence on the lumbar spine 
stiffness represent qualities of the model. 
3 Results 
The three physiological posture of the lumbar spine (flexion, extension, rotation) were measured on a 
part of one cadaveric lumbar spine (L1-L5). Range of motion was controlled by the spine fixator in 
interval (+ 5.3 : -6.3 deg) by flexion/extension. Specimen was loaded just in one direction up to the 
maximal angle of +1.3 deg in torsion [9]. The response of the specimen [Nm] was measured and the 
stiffness was determined. Maximal stiffness in flexion was approximately 3.5 [N.m.deg-1], in extension 
0.5 [N.m.deg-1] and in torsion 1.6 [N.m.deg-1]. These values are in very good accordance other 
measurements [9]. Increasing rotation angle means increase of ligament loading moment, on the other 
hand the stiffness decreases (figures 3 and 4). The reason for this behaviour is given by the properties 
of cadaveric ligament, whose sti ffness is decreasing by gradual rotation and itself becomes more 
elastic [5]. 
0
0,1
0,2
0,3
0,4
0,5
0,6
0,7
0,8
0,9
1
0 1 2 3 4 5 6 7
j [deg]
M [Nm]
flexion
extension
torsion
 
Figure 3 - Graph of motion in flexion, extension and torsion. 
 
  
0
0,5
1
1,5
2
2,5
3
3,5
4
0 1 2 3 4 5 6 7
j [deg]
K [Nm/deg]   
flexion
extension
torsion
 
Figure 4 - Graph of stiffness in flexion, extension and torsion. 
4 Conclusions  
Mechanical testing of cadaveric spine is the best method of investigating mechanical function and 
failure of the spine. Real artificial models are more suitable for investigation of kinematic processes, 
such as segment response to its loading. FEM models can be used to explain experimental results, 
but their predictive power is limited by inadequate knowledge of the material and movement properties 
of spine tissues. Two main parts of soft tissue affect mobility  of the whole spine (intervertebral discs, 
ligaments). The mechanical properties of cadaveric spines reflect the in-vivo properties. The 
Specimens should be kept moist during testing. Testing by 21°C is usually acceptable. Number of 
specimens shouldnt be less than six [10] to obtain adequate results. The shortcoming of our 
measurement was limited number of specimens. The availability of the human spine represents a big 
problem for this experimental study. Therefore for further experiments a new artificial spine will be 
developed. It is being developed in cooperation together with doctors from Motol University Hospital in 
Prague and University Hospital Aachen- Medical Faculty RWTH  and experts from the Institute for a 
materials science RWTH Aachen. The preliminary results are in very good accordance with literature 
and therefore the proposed method can be used for human lumbar spine stiffness determination. 
Acknowledgements 
The research is supported by the Czech Science Foundation: Research of biocompatible materials 
that are useable for production of new type of total intervertebral disc replacement, No. 106/05/2174 
and by the Ministry of Education project: Transdisciplinary research in Biomedical Engineering II, No. 
MSM 6840770012. 
References 
[1]  Nachemson, A.L. and Evans, J.H. (1968) Some mechanical properties of the third human lumbar 
interlaminar ligament (ligamentum flavum). J. Biomechanics 1, 211-220  
[2]  Waters, R.L. and Morris, J.M. (1973) An in vitro study of normal and scoliotic interspinous ligaments. J. 
Biomechanics 6, 343-348 
[3]  Cyron B. M. and Hutton , J.H. (1981) The tensile strength of the capsular ligaments of the apophyseal joints. 
J. Anat. 132, 145/150 
[4]  Panjabi, M. M., Goel, V.K. and Takara, K. (1982) Physiologic strains in the lumbar spinal ligaments. Spine 7. 
192-203 
[5]  Pintar, F. A., Yoganandan, T.M., Elhagediab, A. (1992) Biomechanical p roperties of human lumbar spine 
ligaments. J. Biomechanics 25, 1351-1356 
[6] Morlock, M. M., Bonin, V. (2000) Determination of the in vivo loading of the lumbar spine with a new 
approach directly at the workplace  first results for nurses,  Clinical Biomechanics 15, pp. 549-558 
  
[7] Steffen, T., Rubin, R. (2002) 3-D Lumbar Spinal Kinematics Measurements: Method, Validation and Results, 
McGill University Orthopaedic research laboratory, Canada 
[8] Bergmann, G. (1999) Load Measurements at Spinal Fixators, Free University of Berlin, Benjamin Franklin 
School of Medicine, Biomechanics Laboratory, Berlin, Germany  
[9] Schendel,J., Wood,B. (1993) Experimental measurement of ligament force, facet force and segment motion 
in the human lumbar spine. J. Biomechanics 26, 427-438  
[10] Wilke,J., Wenger,K. (1998) Testing criteria for spinal implants: recommendation for the stansardiyation of in 
vitro stability testing of spinal implants. Ero spine 7, 148-154  
[11] Adams,M., (1995) Mechanical testing of the spine. Spine 20, 2151-2156 
[12] Hall,H., (1996) Save your aching back and neck  
 


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